David Blunkett, the former Labour cabinet minister, has strongly questioned Ed Miliband's leadership credentials, saying he cannot recall a single thing the younger Miliband has said in the past three months that has represented a "challenge" to the party or the country.

In an interview with the Guardian Blunkett also criticised the 2010 Labour election manifesto for which Miliband junior had responsibility, saying it looked as if it had been written on Sunday morning and was "deeply uninspiring ... it is a bit rich for those that were in what they amusingly call the Brown bunker to claim it was nothing to do with them, and it would be nice if we suddenly became radicals".

Blunkett, the former home secretary and one of Labour's most senior MPs, has nominated Andy Burnham as his first preference in the contest, saying he wanted his authentic working class voice in the campaign. But Burnham is thought to be trailing the Miliband brothers.

Blunkett said: "I am very strongly in favour of people casting their second preference for David Miliband. It is absolutely crucial for the future of the Labour party and the country that someone with the experience and grasp of global challenges should lead the party, and that clearly would be David."

Ed Miliband's campaign said at the weekend it was picking up the bulk of second preference votes. "I know Ed Miliband would vehemently object to being painted as a left-leaning comfort zone, since I have put it to him," Blunkett said.

"But I have to ask the question, what difficult challenge has Ed put to the party, or to the electorate during the last three months, and I cannot think of one."

Blunkett also urged the party to recognise the scale of the challenge it faced: "It is a delusion to think that the coalition will collapse even if as many as 10 Liberal Democrat MPs defect to Labour or go independent." He added: "We have to be brutally honest with ourselves about what it will take to beat the coalition that may well stand as a national progressive coalition at the next general election, whether Simon Hughes [the leftwing Lib Dem deputy leader] likes it or not."

Blunkett is concerned that the process of the leadership election has led some candidates to think too much in terms of what the party, as opposed to the country, thinks.

In further criticism directed at Ed Miliband, he said: "It was decisions such as the 10p tax rate that had far more to do with the disillusionment with Labour in the 2010 election than the Iraq war, or a too casual approach to civil liberties or graduates paying back their fees.

"There is a very real danger that we have seen terminology used in the campaign that is reminiscent of Alice Through the Looking Glass, with phrases like 'the comfort zone of New Labour'. I don't want any comfort zone and I don't want to benchmark us against New or Old Labour.

"I want us to benchmark ourselves against the challenges of 2015 and 2020, but if anyone thought New Labour was a comfort zone, they did not live through it. We were constantly being challenged to debate and to take decisions with which we were deeply uncomfortable and that is the job of a leader.

"A leader is not someone who tests the water about how people feel in a party and then articulates the loudest voice at that moment. It is someone who looks ahead and then does his upmost to persuade and cajole his supporters to look ahead."

Blunkett added: "Take a constituency like Reading West, where many people live on £20,000 a year. You have to ask yourself what made them vote Conservative – their concerns were not necessarily the concerns of the most active members of the Labour party and that is the terrible historic dilemma for the Labour party.

"What we feel and what the key swing voters feel is not always the same, and in a democracy you ignore that at your peril. For instance, if you turn away from the electorate on issues like crime and terrorism, the voters will turn away from you. It was not the electorate that got it wrong, and it took the Conservative party at least two or three attempts to learn that lesson."

He said that, before the election and in the manifesto: "We should have been challenging about how we deal with the deficit whilst still massively reforming the welfare state, retaining universality but asking the question whether people on very high incomes can surely afford to have their winter fuel allowance or their child benefit included in taxable income. That is something that would have resonated with people, difficult as it is.

"So we missed an opportunity to say this is a very difficult moment when we are asking you to help us face the biggest challenge since wartime but we are going to do it with a radical bent with a vision for the future."

He said Labour initially had an understanding of the defeat but "there has been a drift away as they have gone to meetings where the pressures of the faithful are slightly different to the electorate as a whole".

He added: "You would have thought the centre-left in politics would have been the beneficiaries of the global meltdown, the collapse of financial markets, especially since it was politics that saved us from the worst outcome, yet it has been the opposite.

"Collectively across the world there has not been a narrative from the centre left. The Democrats in the US are in virtual meltdown and only two left parties govern in Europe, so the outlook is that we have to rebuild a belief in politics."